To simply and certainly set a form even in a narrow work space by providing an inner cylindrical part capable of being screwed in the attaching hole formed to the form and the outer cylindrical part of which the leading end is present at a position retreating from the leading end of the inner cylindrical part so as to provide a gap outside the inner cylindrical part.

An insert holder 40 is integrally molded from a resin and a groove 33 is provided to the inside of an inner cylindrical part 31 in the vicinity of the leading end 32 thereof in order to fit an attaching part 39 in the boss 50 attached to a form 60. Since the leading end 32 of the inner cylindrical part is provided at a position retreating from the leading end 36 of an outer cylindrical part, the leading end 36 of the outer cylindrical part strikes against the inner surface 62 of the form prior to the leading end 32 of the inner cylindrical part and the force due to the distance difference between them is entirely applied to the leading end 36 of the outer cylindrical part. Since there is a gap 34 between the outer and inner cylindrical parts 35, 31, the inner cylindrical part 31 is easy to deform and the outer cylindrical part 35 strikes against the inner surface 62 of the form to achieve function preventing the penetration of the lime wash of concrete. Even if the protruding height from the inner surface 62 of the form is low, an insert metal fitting can be strongly set.